Blood purification systems, which are used for conducting hemodialysis, hemodiafiltration or hemofiltration, involve the extracorporeal circulation of blood through an exchanger having a semi permeable membrane. Such systems further include a hydraulic system for circulating blood and a hydraulic system for circulating replacement fluid or dialysate comprising the certain blood electrolytes in concentrations close to those of the blood of a healthy subject. Most of the conventionally available blood purification systems are, however, quite bulky in size and difficult to operate. Further, the design of these systems makes them unwieldy and not conducive to the use and installation of disposable components.
Standard dialysis treatment, using an installed apparatus in hospitals, comprises two phases, namely, (a) dialysis, in which toxic substances and scoriae (normally small molecules) pass through the semi-permeable membrane from the blood to the dialysis liquid, and (b) ultrafiltration, in which a pressure difference between the blood circuit and the dialysate circuit, more precisely a reduced pressure in the latter circuit, causes the blood content of water to be reduced by a predetermined amount.
Dialysis procedures using standard equipment tend to be cumbersome as well as costly, besides requiring the patient to be bound to a dialysis center for long durations. While portable dialysis systems have been developed, conventional portable dialysis systems suffer from certain disadvantages. First, they are not sufficiently modular, thereby preventing the easy setup, movement, shipping, and maintenance of the systems. Second, the systems are not simplified enough for reliable, accurate use by a patient. The systems' interfaces and methods of using disposable components are subject to misuse and/or errors in usage by patients. For a portable dialysis system to be truly effective, it should be easily and readily used by individuals who are not health-care professionals, with disposable input and data input sufficiently constrained to prevent inaccurate use.
One conventional design of dialysis systems uses a single pass system. In single pass systems, the dialysate passes by the blood in the dialyzer one time and then is disposed. Single pass systems are fraught with a plurality of disadvantages, arising from the use of large amounts of water. First, assuming a 50% rejection rate by the R.O. (Reverse Osmosis) system, at least 1000 to 1500 ml/min of water is required. Second, a water purification system for providing a continuous flow of 100 to 800 ml/minute of purified water is required. Third, an electrical circuit of at least 15 amps is required, in order to pump 100 to 800 ml of water/minute, and, fourth, a floor drain or any other reservoir capable of accommodating at least 1500 ml/min of used dialysate and RO rejection water.
Conventional systems are also less reliable because of the necessity of using a myriad of tubes comprising the fluid circuits of the purification systems, thus increasing the risks of leakage and breakage. In addition to being difficult to transport due to their large size, conventional dialysis machines also suffer from a lack of flexibility. For example, sorbent based hemodialysis procedures have a particular set of hardware requirements that are not shared by the hemofiltration process. Thus, it would be beneficial to have common hardware components such as the pumping system, which can be used such that the dialysis system can be operated in hemofiltration as well as hemodialysis modes.
Additionally, there is a need for a portable system that can effectively provide the functionality of a dialysis system in a safe, cost-effective, and reliable manner. In particular, there is a need for a compact dialysis fluid reservoir system that can satisfy the fluid delivery requirements of a dialysis procedure while integrating therein various other critical functions, such as fluid heating, fluid measurement and monitoring, leak detection, and disconnection detection.
With respect to disconnection detection in particular, the effective detection of a return line disconnect is difficult, as most known methods are based on monitoring and detecting a change in pressure in the venous return line tubing. Return line disconnection usually occurs due to a needle pull out situation. Since a needle typically offers the highest fluidic resistance in an extracorporeal blood circuit, a pressure change in the return line due to needle disconnect is not significant and cannot be detected easily. The pressure drop is also very low in cases where a catheter disconnects from a patient's body, causing a return line disconnection. Hence, detection of a disconnection in a return venous blood circuit using pressure as an indicator or metric is unreliable and may result in serious injury. Further, methods using detection of air bubbles as an indication of a disconnect cannot be relied upon because a disconnect in a venous return line does not cause air to be drawn in the return line tubing. Consequently, there is need for an improved apparatus and method for detecting a disconnect in a venous return line. Further, there is also need for an apparatus and method which does not require any extra element, such as a moisture pad to be placed at the needle insertion site.
Additionally, there are no satisfactory mechanisms in the prior art for maintaining volumetric accuracy during the dialysis process that can be easily implemented at a reasonable cost. Most of the prior art methods for maintaining volumetric accuracy of replacement fluid and output fluid are not suited for use with disposable devices. One prior art approach for maintaining volumetric accuracy involves weighing both the replacement fluid and output fluid. However, this approach is difficult to implement in practice. Another prior art method comprises the use of volumetric balance chambers for dialysis systems. Such chambers are, however, complex and expensive to build and also not suitable for disposable devices. Volumetric flow measurements are another known method, but the accuracy of this method is not proven. Further, this method is very difficult to implement for a dialysis system in disposable form. Another prior art approach involves using two piston pumps to achieve volumetric accuracy. However, this approach is extremely difficult to implement at a reasonable cost in disposable form, and is also not economical to operate at the required pumping volumes, which are of the order of 200 ml/min. There is therefore a need for a method and a system that can be used to accurately maintain the volume of the fluid infused into and removed from the patient, and which can be implemented inexpensively.
Furthermore, there is a need for a multiple-pass sorbent-based dialysis system that lowers the overall water requirements relative to conventional systems. There is also a need for a manifold that can be used in a single pass sorbent-based dialysis system as well as in the multiple-pass system of the present invention, which offers a lightweight structure with molded blood and dialysate flow paths to avoid a complicated mesh of tubing.
It is also desirable to have a portable dialysis system that has a structural design configured to optimize the modularity of the system, thereby enabling the easy setup, movement, shipping, and maintenance of the system. It is further desirable to have system interfaces, through which patients input data or deploy disposable components, configured to prevent errors in usage and sufficiently constrained to prevent inaccurate use.